Prop trouble

[benzatech]

Patch coming undone gonna try to repair with resin and remove patch, if not what and where should i get a prop. I think its 78 inch. First airboat thanks.in central fl area

 

[Gary S]

Send it back to manufacture. I wouldn't run it .

 

[benzatech]

thanks Gary, So im gonna send it back to get repaired got a replacement pair of props that I put on there, but having lots of trouble getting pitch dialed in. the prop I removed used to move me real easy and get on a plane. this new prop wouldnt even move me. so Im gonna put on the trailer and chalk the tires and tire to set the prop by RPM. so at idle it should spin about at 1000 rpm and at WOT be around 3300? its a DD 350 with a cam im told. no gear box or belt. nothing fancy about the 350 except it leaks lol. trying to get it dialed in, spent about 2 hours on the lake today trying to fiddle with it and got a little better but more like the blind leading the blind.

 

[One Eyed Gator]

How long is your prop?
72" prop at 3,300 is a tip speed of 707mph, mach is 772 mph of a 75degree day your turning 93% of that number

I would be care much faster and even at the tip speed bad thing start to happen

Could be why your patch is delaminating

 

[benzatech]

So what your saying is 3300 wot is too high and should be alot lower. Which means i have next to no pitch in it to get that high of an rpm at WOT. I believe on my old prop i was on a plane and moving fast at like 2300 or 2400 rpm something like that.

 

[One Eyed Gator]

Yes lower RPM would require more pitch
Setting the lower you will loose snap but will stay on plane at a lower RPM

Finding the sweet spot is kind of compromise between snap and lower rpm push

Most DD props are pitched 2800-3000 rpm

 

[benzatech]

Thanks. Turns out the old props are too old to be repaired. So im stuck with spare props i think. I guess snap is acceleration? Gonna try and dial it in around 2900 at wot on trailer.

 

[One Eyed Gator]

Snap is how quick it spins up

 

[Slidin Gator]

Thanks. Turns out the old props are too old to be repaired. So im stuck with spare props i think. I guess snap is acceleration? Gonna try and dial it in around 2900 at wot on trailer.

What is the spare now main prop? Make, Model, Diameter, Year? Post some pics.

2,900 rpm is the most you should be spinning, that's where my 72" prop spins right now and I need to add some pitch.

 

[benzatech]

Basically almost identical replacement, that i had bought as a spare prop to use while the damaged prop was repaired. Now that it cant be repaired, so the spare prop i had on is now the only prop i can use. I basically got screwed when i bought this airboat with a damaged prop, but hey lesson learned. The prop i have on there is a little newer but still used. I think they are called bowtie props? Wind walker?

 

[benzatech]

Its not letting me upload pics due to the file being to large.

 

[Slidin Gator]

You got an old Water Walker prop, now called Carbon Concepts. Good props for sure, but even the prop you are running now is running out of life.

Measure the diameter, tape measure end to end, this is the critical info for more input.

 

[benzatech]

72 inches

 

[Slidin Gator]

That prop likes about 2,800 RPM with a torque making engine. The prop manufacturer rates it for 2,800 max. On the other hand, a direct drive 350 needs to turn all she can. I would not run a new one over 3,000 and given the age I suggest you dial it in at 2,800 and get what you get.

The prop itself is pretty wide for a DD 350 and at 72" you are running a lot of prop, too much without specific engine work. The more ideal prop for that setup would be 66-68" diameter, which will spin up quicker and can run a bit more RPM to make the engine happier.

 

[benzatech]

Gotcha thanks, I had someone else say something similar and to go to a 6 blade. If these need to be replaced ill shop in that range. When setting pitch, what degree angle should i start out at?